The measurement of temperatures and expansions on rotatable parts, such as drive shafts and generator shafts for example, is becoming increasingly important since, as a result of ever higher power demands, these parts will be operated right up the their load limits. As a rule conventional electrical temperature sensors, such as thermoelements for example, and electrical expansion sensors, such as piezoelectric sensors for example, are used for this purpose. In such cases the sensor signals must be conditioned to the shaft. This is normally done with special measurement amplifiers. Radio transmission or IR transmission is then used to send the measuring signals conditioned using this method from the shaft to a transceiver unit located in a fixed position in relation to the shaft. For this purpose auxiliary energy must be provided on the shaft in each case to enable the electronic components arranged there to be driven. This can be done for example through a battery or also through an inductive transmitter. Overall a large outlay is involved here. Since enormously high centrifugal forces can arise with shafts rotating at high speed, the corresponding electronic components must be adapted to these extreme conditions. The electronic components are usually encapsulated.
Instead of electrical sensors, the use of optical sensors based on optical waveguides, such as FBG (FBG: Fiber-Bragg-Grating) sensors, is known for these types of measurements on parts turning at high speeds. In such cases the actions of coupling and decoupling an optical transceiver unit arranged in a fixed location to and from the rotating shaft have proved especially difficult. For example optical transmitters arranged axially on a face side of the rotating shaft are especially suitable for this purpose, employing two collimators to transmit light signals between a transceiver unit arranged in a fixed position relative to the shaft and an optical waveguide arranged on the rotating shaft. In such cases the two collimators are arranged in a common housing which is embodied with one non-rotating and one rotating part. Such an optical transmitter is however not suitable for measurements on shafts for which there is no access to the end face side.